We propose to continue studies of the structure of the DNA genome bacteriophage phi X 174 by dissecting this molecule with a variety of bacterial restriction endonucleases. We will obtain nucleotide sequences from regions of particular genetic interest. We will develop generally useful techniques for mapping restriction fragments by a two-dimensional hybridization procedure. This procedure will be applied to mapping phi X 174 restriction fragments. BIBLIOGRAPHIC REFERENCES: Potter, S., Newbold, J., Hutchison, C., and Edgell, M. Specific Cleavage Analysis of Mammalian Mitochondrial DNA, Proc. Natl. Acad. Sci. U.S.A., in press. 1975. Edgell, M., Hutchison, C., and Bott, K. Are the Same Cistrons Used to Code for the Ribosomal RNA in Vegetative Cells and Sporulating Cells of B. Subtilis? Spores VI, ed. Gerhart, Sadoff and Costilow. Am. Soc. Microbiol. 1975.